Purification of organic solvents containing metals by peroxide wash

ABSTRACT

A METHOD FOR THE REMOVAL OF RESIDUAL METALS, SUCH AS COPPER, FROM FOULED ORGANIC SOLVENTS, SUCH AS AMINES, WHICH ARE USED IN SOLVENT EXTRACTION PROCESSES, IN WHICH THE METAL-CONTAINING AMINE IS CONTACTED WITH AN AQUEOUS STRIPPING CONTAINING DILUTE CONCENTRATIONS OF A SOLUBLE PEROXIDE.

y 23, 1972 E. WIGSTOL 3,664,815

PURIFICATION OF ORGANIC SOLVENTS CONTAINING METALS BY PEI (OXIDE WASHFiled Dec. 12, 1969 PURIFIED ORGANIC LIQUID EXTRACTION STRIPPING CIRCUITCIRCUIT A ACIDIC METAL AQUEOUS STRIPPING BEARING AQUEOUS SOLUTIONCONTAINING CHLORIDE SOLUTION HYDROGEN PEROXIDE CONTAINING COPPER FIG. 'I

PURIFIED ORGANIC LIQUID FIRST SECOND EXTRACTION STRIPPING STRIPPINGCIRCUIT CIRCUIT CIRCUIT 'IHHITIAHAH) ACIDIC METAL AQUEOUS STRIPPINGAQUEOUS STRIPPING BEARING AQUEOUS SOLUTION WITHOUT SOLUTION CONTAININGCHLORIDE SOLUTION HYDROGEN PEROXIDE HYDROGEN PEROXIDE CONTAINING COPPERFIG. 2

INVEN'IOR. EIVIND WIGSTOL ATTORNEYS 'U.S.' o1. 23- 3123 a s u l was e cnn ra a fl me United States Patent I iEivind'Wig'st'ol,'fKristiansaitds, Norway, assignor to Falconbridge l$lickelMines Limited, Toronto, Ontario,

' 7 Canada "FiledDec. I2, 1969, Ser. No. 884,406

Int. (31113016 11/04; C01g 3/04 I 7Claims theducted-containingaminersc'o ntacted with an aqueous stripping lution contai ng "diluteconcentrations of The iriventionilrelates to the general field ofsolvent extractiommore particularly tothe purification of fouled,organic solyents used;for'theextraction of metals from,aqueous.solutions andspecifically to the regeneration of fouled aminescontaining copper extracted from acidic aqueous chloride solutions.

In solvent extraction processes in which the solvent is cycled insequence through extraction and stripping, i.e. back extraction,operations, the effective capacity of the solvent is less than themaximum if any extracted ions remain unstripped and are returned thereinto the extraction. operations.. Eurthermoresincejgthere is anequilibrium distribution of tanyg met-al betweerran organic solvent andan aqueous solution-in ontact it is clear that the higher A .n;-t hesolvent, the higher rthe.concentration-o fhatsamernetal in the aqueoussolutioii. Thus it is readily understood that to extract substanenteringa counter-current solvent extraction system with that aqueous so utionshould also be substantially devoid n ma metal in question; Conversely,if the ,rqsidualtmet-als -in the solvent is allowed continualcyclingthereof, it is clear that the efiiciency of the solvent forextraction of those metals will becorrespondinglydecreased. Such is thecase with the extraction,of,copper from ,acidic aqueous chloridesolutions into i 'nes when stripping is done with Water or idiliiteaqueous-[chloride solutions.

' To illus nature of the-problem to which the present mention is"directed, reference is made to US.

Pat. No. 3,085,054 inwhich a process is described for the recovery ofnickel from copper-nickel matte. The matte is finely-divided andleachedin hydrochloric acid solution to dissolvenickel;preferentially;with..respect} to copper thereby produc g arlacidic niclil'chlbride solutiorfiand; a

art-insoluble co erfs ulphide residue. The nickelchloride solutioncontains so'mo copper and also small concentration s o'f other metalspresent in the matte such as iron, cobalt, lead and zinc. To purify thissolution priorato recovery .of. themickel chloride;therefrom, thesolution is, v first contacted. witgh oxygen or- -chlorine to oxidizeiron,

3,664,815 Patented May 23, 1972 (TBP), and subsequently the cobalt andcopper are extracted together in tri-iso-octylamine (TIOA). In additocobalt and copper the TIOA also picks up iron not extracted in the TBPcircuit and also some zinc. The TIOA is then contacted with water tostrip the extracted metals therefrom and the stripped TIOA is thenrecycled for extraction of further quantities of cobalt and copper fromthe nickel chloride leach solution.

It can happen that not all the extracted metal is stripped from TIOA andthat residual concentrations of copper, iron and zinc circulate thereinand increase with each cycle thereby continually decreasing theextraction efiiciency of the TIOA with respect to copper, iron and zinc.

Past efforts to remove residual metals from the TIOA, particularlycopper, have been unsuccessful. For example some residual iron wasstripped by washing of the TIOA with water but the pickup of zinc wasonly arrested and removal of copper was negligible. Some copper wasstripped by caustic but iron remained in the TIOA and a bulky slimeprecipitate was formed that was difiicult to filter. This precipitatewas dissolved in HCl but both the HCl and NaOH were consumed and thetreatment was therefore not only incomplete but costly. Nitric acidalone was ineffective in cleaning the TIOA because metal nitrates wereextracted thereby and were stripped only by contacting the TIOA with abase such as caustic, another costly procedure.

Thus there has not been until now any practical means to purify TIOAfouled by residual copper' and other metals. The same applies to otheramines that will extract copper from acidic aqueous chloride solutionsas anionic chloride complexes.

It has now been found that the concentrations of residual copper andother metals in the amine after stripping can be made negligible whenthe amine is contacted with an aqueous solution containing diluteconcentrations of a soluble peroxide.

SUMMARY In a cyclic solvent extraction process for treating an acidicmetal-bearing aqueous chloride solution containing copper anionicchloride complex for removal of copper therefrom comprising bringing thesolution into contact with an amine solvent for copper anionic chlorideCOll'lplex dissolved in a substantially Water-immiscible organic carrierliquid, extracting copper into the solvent, separating the organicliquid and aqueous solution, bringing copper-bearing solvent intocontact with one or more aqueous stripping solutions, stripping copperinto the solutions thereby depleting the solvent of copper, separatingthe organic liquid from each stripping solution in turn, and reusing thecopper-depleted solvent for treating fresh quantities of the acidicmetal-bearing aqueous chloride solution, the present invention statedbroadly comprises bringing the copper-bearing solvent into contact withan v aqueous stripping solution containing a soluble peroxide therebyremoving copperfrom the solvent and controlling cumulation of residualcopper therein, s

"By' this means the solvent can be substantially completely depleted .ofcopper when a water-soluble peroxide '"comp rises part of an aqueousstripping solution.

' The object of this invention is to providemeans to pu'rifyfouledorganic solvents used in the solvent extraction of metals from aqueoussolution, specifically amines fouled with copper.

Other objects and advantages'of the invention will be apparent'from thefollowing description taken conjunction with the accompanying drawings.

3 BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a flowsheet of a solventextraction process in which an embodiment of the present invention iscarried out.

FIG. 2 shows another flowsheet illustrating a modification of theprocess of FIG. 1 that is within the scope of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates, by way of afiowsheet, an embodiment of the present invention in a conventionalmultistage counter-current solvent extraction system. An acidicmetal-bearing aqueous chloride solution containing copper as anionicchloride complex is brought into contact in a three-stagecounter-current extraction circuit with an amine solvent for copperanionic chloride complex dissolved in a substantially water-immiscibleorganic carrier liquid. The copper is extracted into the amine and theorganic liquid containing the amine is then separated from the aqueoussolution. The copper-bearing organic liquid is then brought into contactin a three-stage counter-current stripping circuit with an aqueousstripping solution having hydrogen peroxide dissolved therein. Thecopper is stripped into the stripping solution and the resultingsubstantially copper-free organic liquid is separated therefrom andreturned to the extraction circuit.

The fiowsheet of FIG. 2 illustrates an alternative procedure within thescope of the invention. In this case the copper-bearing organic liquidis brought into contact in a three-stage counter-current strippingcircuit with a first aqueous stripping solution that does not containhydrogen peroxide or any other peroxide. Stripping of the copper istherefore not necessarily complete and the copper-depleted solvent canthus retain residual copper. The copperdepleted solvent is then broughtinto contact in another three-stage counter-current stripping circuitwith an aqueous solution that does contain hydrogen peroxide. Residualcopper is thereby stripped from the solvent and the cleaned solvent isreturned to the extraction circuit as in the procedure illustrated inFIG. 1.

The choice of whether the peroxide is in the first or subsequent aqueousstripping solutions depends on whether metal ions other than copper,that might also be accumulated in the organic liquid and might bestripped therefrom by the action of the peroxide, could be tolerated inthe first aqueous stripping solution, in which the majority of thecopper is present. If not, then an alternative such as that illustratedby the flowsheet of FIG. 2 is indicated.

While continuous treatment of the organic liquid with peroxide -isadvantageous in those cases in which a tendency is observed for residualconcentrations of copper to accumulate theerin, it is by no meansessential to the successful practice of the invention. Residual metalcan be permitted to accumulate and then be eliminated periodically byoccasional washing with the peroxide solution.

Since peroxides are well known oxidants it might be thought that theirfunction in the present application is one of mere oxidation therebyimplying the presence of cuprous ions in the organic solution thatbecome oxidized according to a reaction such as, in the case of hydrogenperoxide:

This thought implies further that copper is extracted into the organicliquid in both the cuprous and the cupric state but that cupric copperis stripped therefrom more readily by dilute aqueous solutions, therebyleaving behind a residual copper concentration of cuprous ions.

Whether the latter implication is true or not the behaviour of peroxidein the present instance does not conform to the obvious mechanismsuggested above, and is in fact unknown. Surprisingly it has been foundthat copper is removed from the organic liquid by contact with much lessperoxide than the stoichiometric requirement of the above reaction andfurthermore that dilute concentrations of peroxide in the aqueousstripping solution are more effective than more concentrated solutionsin the removal of copper from the organic solvent provided, of course,that the absolute quantity of peroxide is suflicient to remove asubstantial proportion of the copper. These phenomena are illustrated inTable 1 by data obtained from shake-out tests in the laboratory usinghydrogen peroxide.

TABLE 1.H2O2 REQUIREMENT, EXPRESSED AS A PER- OENTAGE OF THESTOICHIOMETRIC REQUIREMENT FOR REACTION 1, To REMOVE VARIOUS PROPORTIONSOF RESIDUAL COPPER INTO SOLUTIONS OF VARIOUS H202 CONCENTRATIONSProportion of copper removed, percent Percent of stoichiometric H202H2O: concentration, Wt. percent:

A copper-fouled organic liquid of 10% TIOA dissolved in Solvesso 150 asa suitable organic carrier contained 850 mg./l. of copper. Uniformquantities of this organic liquid were contacted with aqueous solutionscontaining H 0 at concentrations as shown in the above table and at avariety of organic to aqueous ratios to provide data for a range of Cuto H 0 ratios. No precipitates were formed on shaking and the two phasesseparated cleanly on settling. The organic was then analyzed for Cu todetermine the degree of copper removal and the above data indicate thoseconditions under which the amount of H 0 contacted was less than thatrequired according to the stoichiometry of reaction 1 to account for thedegree of copper removal achieved.

Thus while 70% of the copper was removed in a 0.5% H 0 solutioncontaining 70% of the stoichiometric amount of H 0 required for 100%removal of Cu according to reaction 1, of the copper was removed in a0.125% H 0 solution containing only 50% of the stoichiometric amount ofH 0 required for Cu removal on the same basis. These results aresurprising for two reasons, not only because the effectiveness of the H0 in removing copper from the organic solution varies inversely ratherthan directly with its concentration but also because the mechanism ofits function is apparently not mere oxidation of cuprous copperaccording to reaction I as might have ben expected.

Further illustrations of the practice of this invention are provided inthe following examples.

Example 1 An acidic aqueous chloride solution containing mainly nickel,cobalt, copper and hydrochloric acid was brought into contact with TIOAdissolved in Solvesso in a continuous counter-current system, cobalt andcopper were preferentially extracted together with hydrochloric acid andminor quantities of nickel and other metals such as iron and zinc,nickel was stripped from the TIOA in a concentrated hydrochloric acidsolution, copper was stripped in a subsequent water stripping solution,and the TIOA containing residual copper and other metals wasrecirculated to the extraction circuit. After some time, the copper andother residual metals had accumulated to such as extent that about 30%of the extractive capacity of the TIOA was unavailable for extraction offresh quantities of metal. A period followed in which the TIOA wastreated with water after the copper-stripping stage, and subsequentlythe water treatment was replaced by a similar treatment with watercontaining 0.4% H 0 The average concentrations of copper in the organicat the end of each period are shown in Table 2.

TABLE 2 Effect of various purification treatments on residual coppercontent of TIOA Name and duration of treatment: Cu concentrations 1Before purification 700 8.5% TIOA dissolved in Solvesso 100 2 H O310116, 3 days 460 lligfore pulrlificitfionut 91;

- er was Wl wa er H202 Solutions 3 days 2 After Wash with water having0.3% H 2". 1.6 1.3

After wash with water having 6.9 g.p.l. Na2O2 1.4 2. 5

1 At end of each period, mg./l.

It is clear from the table that while only a portion of the copper wasremoved by washing with water alone, the

copper was substantially completely removed by treatment with theperoxide solution.

The results indicate that the concentrations of copper can be maintainedat low levels advantageously by the presence of a small concentration ofa soluble peroxide in an aqueous stripping solution. Under thesecircumstances the organic liquid can be recycled continuously with highextractive capacity for copper and other metals from the acidic aqueouschloride solution.

Example 2 A series of tests was made to investigate the effectiveness ofhydrogen peroxide in cleaning and regenerating copper-fouled aminesother than TIOA. Various solvents were mixed with Solvesso 100 to makeorganic liquids containing 10% solvent and each was treated with ahydrochloric acid solution containing cuprous chloride. Each resultingcopper-bearing organic liquid was then stripped with water to simulatecopper stripping in practice and was then divided into two equal partsof 250 cc. each. One part was brought into contact with three 100 cc.lots of water in succession and the other part with three 100 cc. lotsof water containing 0.3% H 0 The effectiveness of water alone and ofwater containing H 0 in removing residual copper from these organicliquids is contrasted in Table 3.

TABLE 4.EFFECT OF VARIOUS AQUEOUS SOLUTIONS ON REGENERATION OF FOULEDTIOA Cu concentrations in organic liquid before and after treatment,mgJl.

Series 1 Series The results indicate not only that the purified organicliquid was substantially copper-free but also that the sodium peroxidesolution was substantially as effective for copper removal as was thehydrogen peroxide solution. Thus it is reasonable to suggest that anywater-soluble peroxide would be similarly effective in the removal ofcopper although hydrogen and sodium peroxide are the only two that wouldlikely be used commercially.

While the organic carrier liquids that have been used most extensivelyin the present work are Solvesso 100 and 150, the method is not limitedto these carriers. Test- Work has shown that the carrier acts only as adiluent and does not aifect the equilibria between the organic solventand aqueous phases.

In solvent extraction systems such as the present one, which employmixer-settler equipment, the most suitable carriers for amine solventsare aromatics such as methyl benzenes (xylenes) and their derivatives.Some chlorinated hydrocarbons could also be used. Aliphatic carrierssuch as kerosene would be satisfactory as far as the effect of peroxideon the regeneration of dissolved amine solvents is concerned, but theyform a second organic phase after heavy loading and therefore are notsuitable for use with mixer-settler equipment. In general any carriershould be satisfactory in the present and similar systems if it issubstantially immiscible in water and forms only one TABLE 3.-EFFECT OFWATER AND H202 soLt rg ogt s oN PURIFICATION OF AMINES FOULED WITHSolvent Percent removal of No. of C atoms residual copper I in R groupsClassification Identifying In H2O In H202 of amine trademark Chemicalname Individual Total alone solution Secondar {Amberlite LAl N-dodecenyl(tzialkyl methyl) amine 12, 12-15 24-27 33. 0 98. 8 y Amberlite LA2N-lauryl (tri alkylmethyl) amine 12,13-16 25-28 22. 5 70. 0 Tertia 1{Alamine 336 Tri caprylyl amine 8-12 245-36 25.1 99. 1 r5 Adogen 381 Triiso-octyl amine s 24 27. 7 s9. 7 Quaternary {Aliquat 336 Tri caprylylmonomethyl ammonium chlori e 1, 8-12 25-37 14. 6 37. 5 Aliquat 336 Tricaprylyl methyl ammonium chloride 1, 8-12 25-37 9. 9 47. 4

* For the purposes of this specification secondary, tertiary, andquaternary amines such as those shown above are schematicallyrepresented by the general formulae respectively. To be useful assolvents in solvent extraction each R, R1, R2 and R3 group shouldcontain between 1 and about 20 carbon atoms and the total number ofcarbon atoms in the amine should be between about 8 and about 40. Withfewer than about 8 carbon atoms losses of solvent by dissolution inaqueous solutions can be excessive and with more than about 40 carbonstoms the solvent is generally too viscous to permit ready separationfrom the aqueous solution with which it is in contact. Within theselimits, however, the R, R1, R2 and R3 groups in any given solvent can bealike or different, straight or branched chain, saturated or unsaturatedand may be alkyl, aryl, alkaryl or aralkyl. It is clearly demonstratedthat water containing hydrogen peroxide is much more efiective thanwater alone in the regeneration of all the amines and that theseperoxide solutions are particularly suited to the treatment of secondaryand tertiary amines.

EXAMPLE 3 Other tests were performed to compare the effect of sodiumparoxide solutions with those of hydrogen peroxide. The organic liquidwas an 8.5 solution of TIOA in Solvesso 100. A 350 cc. lot of thisliquid containing residual copper, was given three successive washeswith 100 cc. lots of a given aqueous solution. The initial and final Cuconcentrations in the organic liquid are shown in Table 4.

completely stripped therefrom by aqueous solutions.

What I claim as my invention is:

1. In the method of treating an acidic metal-bearing aqueous chloridesolution, containing copper anionic chloride complex, for removal ofcopper therefrom comprising bringing the solution into contact with anamine solvent for copper anionic chloride complex dissolved in asubstantially water-immiscible organic carrier liquid, said amine beingselected from the group secondary, tertiary, and quaternary amines ofthe general formulae,

11-17141, nz-r r-n R1 R1 respectively, in which each R, R1, R2, and R3group is selected from the group alkyl, aryl, aralkyl and alkaryl andcontains from one to about twenty carbon atoms, and each amine containsa total number of from about eight to about forty carbon atoms,extracting copper into the solvent, separating the organic liquidcontaining the copper-bearing solvent from the aqueous solution,bringing the separated copper-bearing solvent into contact with anaqueous stripping solution, stripping copper into the stripping solutionthereby depleting the solvent of copper, separating the organic liquidcontaining the solvent from the stripping solution, and reusing thecopper-depleted solvent for treating fresh quantities of the acidicmetal-bearing aqueous chloride solution, the improvement in strippingthe solvent of copper comprising bringing copper-bearing solvent intocontact with an aqueous stripping solution having a peroxide selectedfrom the group and hydrogen peroxide and sodium peroxide dissolvedtherein.

2. Method according to claim 1 in which only one aqueous strippingsolution is used.

3. A method according to claim 1 in which at least two aqueous strippingsolutions are used and peroxide is present in at least the secondstripping solution. i

4. A method according to claim 1 in which the solvent istri-iso-octyl-amine.

5. A method according to claim 1 in which the peroxide is hydrogenperoxide.

6. A method according to claim 5 in which the molar ratio of hydrogenperoxide in aqueous stripping solution to copper in copper-bearingsolvent in contact therewit is less than 0.5. e

7. A method according to claim 5 in which the concentration of hydrogenperoxide in aqueous stripping solution is between about 0.1 and about0.5%

References Cited UNITED STATES PATENTS 3,194,652 7/ 1965 Clifford 23-297X 3,337,296 8/1967 Hill 23-97 3,429,694 2/1969 Lower 1 FOREIGN PATENTS69,605 5/ 1969 Germany.

NORMAN YUDKOFF, Primary Examiner S. J. EMERY, Assistant Examiner US. Cl.X.R.

